add filterBySelectAttribute method to page_list

re-implementation of #190 (taking into account @remo's concerns about performance raised in #184)
updated explanatory comment to be more accurate as per @remo
change helper function from private to protected

so it can be overridden more easily (thanks @mkly)
handle an array of mulitple values
small refactor to make code cleaner
refactor: call attribute controller function to determine if multiselect (instead of inline helper function with yucky SQL query)
change to more user friendly error messages. reopen #1137
check for number of months
Let's use the context JobSetName for job set names
Merge pull request #1174 from jordanlev/patch-1

add filterBySelectAttribute method to page_list
Merge pull request #1236 from mlocati/jobsetname-context

Let's use the context JobSetName for job set names
Merge pull request #1232 from Remo/date-archive

check for number of months
Merge pull request #1231 from hissy/better-message

change to more user friendly error messages. reopen #1137
Add support to Windows 8 start screen icons
Merge pull request #1240 from mkly/merge_1223_windows8_start_screen_icons

Add support to Windows 8 start screen icons